Ammunition bullets are characterized by, among other things, caliber and weight. Caliber represents the diameter of the bullet, while weight represents the mass of the bullet. Bullet mass is commonly designated in terms of avoirdupois grain weight throughout the United States.
The flight trajectory and terminal performance of a bullet depend heavily upon the caliber and the weight of the bullet. For example, with other ballistic variables being equivalent, a bullet with a heavier weight sustains its flight velocity better than a lighter weight bullet. The heavy weight bullet, usually launched at a lower initial velocity, drops further from the line of sight than a lighter bullet when fired at the same target. This requires aiming adjustments by the shooter when using ammunition with different weight bullets.
Heavy weight bullets typically penetrate deeper upon terminal impact than lighter bullets, which partially compensates for their lower velocities. Other technical advantages and disadvantages of light or heavy bullets are well known to experienced marksmen.
Marksmen therefore want to know the weight of the bullets in the cartridges they intend to shoot. Differences in bullet weights often are not apparent simply by viewing or handling loaded cartridges. Bullets weights for a common cartridge in its various loadings might vary between 100 and 125 grains. A 25 grain (0.057 ounce) difference is not substantial enough to allow the shooter to quickly or reliably differentiate between two cartridges while holding one of each bullet weight type. Visual determination of bullet weight is not practical because a significant portion of a bullet in a cartridge is obscured by the cartridge casing. Other important bullet characteristics such as construction materials and design features also may not be visibly apparent after the bullet is assembled into a finished cartridge.
Most manufacturers mark ammunition packaging with some indication of bullet weight and perhaps other bullet characteristics. However, packaging markings are ineffective once the bullet has been removed from the package. Moreover, spent casings of cartridges often are reloaded with new cartridge components and the resulting reloads do not necessarily incorporate the proper information to identify the bullet loaded therein.
Some inventions are known whereby bullets convey information. Marking bullets with a system of bands or grooves to indicate bullet characteristics is described in, for example, U.S. Pat. Nos. 1,632,156 and 1,650,908. But, in each situation these marking schemes require marksmen to memorize several different configurations of bands and the corresponding bullet characteristics. Further, such marking systems are not generally known by the shooting public.
U.S. Pat. Nos. 1,887,324, 4,150,624 and 5,485,789 describe bullets having identifiers embedded therein. These inventions offer no help to marksmen because the information is stored inside the bullet and is not visible. Such information generally is of a type not intended for marksmen anyway as such information is usually provided for forensic purposes.